**config.xml** update this :

    <events>
        <mi_productautosynchronization_notifications_before>
            <observers>
                <mi_productautosynchronization_observer>
                    <type>singleton</type>
                    <class>MI_ProductAutoSynchronization_Model_Observer</class>
                    <method>checkMessages</method>
                </mi_productautosynchronization_observer>
            </observers>
        </mi_productautosynchronization_notifications_before>
    </events>


to :

    <events>
        <mi_productautosynchronization_notifications_before>
            <observers>
                <mi_productautosynchronization_observer>
                    <type>singleton</type>
                    <class>MI_ProductAutoSynchronization_Model_Observer</class>
                    <method>checkMessages</method>
                </mi_productautosynchronization_observer>
                <mi_productautosynchronization_test_observer>
                    <type>singleton</type>
                    <class>MI_ProductAutoSynchronization_Model_Observer</class>
                    <method>test</method>
                </mi_productautosynchronization_test_observer>
            </observers>
        </mi_productautosynchronization_notifications_before>
    </events>

  **Observer.php**

    <?php
    class MI_ProductAutoSynchronization_Model_Observer extends Varien_Event_Observer {

    public function test($observer) {
          /*Display the message in the next refresh*/
          Mage::getSingleton('adminhtml/session')->addError(Mage::helper('MI_ProductAutoSynchronization')->__('Error sending Email'));

          // Refresh and display
          // $controllerAction = $observer->getEvent()->getControllerAction();
          // Mage::log("TEST success", null, "dev.log"); // for your logs
          // Mage::getSingleton('adminhtml/session')->addError(Mage::helper('MI_ProductAutoSynchronization')->__('Error sending Email'));
          // Mage::app()->getResponse()->setRedirect($controllerAction->getUrl('*/sales_order/')); //the controller where you want to redirect
          // Mage::app()->getResponse()->sendResponse();
          // exit ; 
          
    }

    public function checkMessages($observer) {
          Mage::log("notification success", null, "dev.log");
          $notifications = Mage::getSingleton('mi_productautosynchronization/notification');
          $notifications->addMessage("I was sent by mi_productautosynchronization");
          return $observer;
    }
    }